To further investigate human auditory motion perception, a series of experiments will be conducted in an anechoic environment, employing a horizontally rotating loudspeaker system for stimulus presentation. Standard psychophysical procedures will be employed requiring subjects to make simple button-press responses to indicate judgments about the various stimuli presented (for example, which of two presented sounds was the moving one?). In the first stage of the project thresholds for the detectability of motion of low-frequency and high-frequency complex sounds will be measured in a variety of listening conditions. In the second stage, the following hypothesis will be explored: that there exists a stage of processing within the auditory system that is specifically sensitive to the horizontal motion of auditory signals. To describe the characteristics of such a motion- sensitive system, several adaptation experiments will be conducted in which a subject's sensitivity to the motion of one stimulus will be measured after the subject has been exposed for a period of time to another moving stimulus (whose spectrum, azimuth, and velocity will be varied). The third stage of the project will explore motion perception in certain non-anechoic environments by studying the interaction of motion sensitivity and the precedence effect. Results from these experiments will describe the limits of humans'ability to detect and discriminate the velocity of horizontally moving sounds. In addition, the results should contribute to our understanding of the mechanisms underlying motion perception by human observers. Such basic knowledge might well have important practical applications for human performance in our dynamic environment.